Animate an emission object appearing and disappearing
You can key the visibility of the object by hovering in the outliner over the render restrict symbol (camera symbol) next to your object and pressing I to add a keyframe. Then create a invisible key on the first frame, a visible key on the second key and again a visible on the third. That should give you the flash effect you want when you render it, but it will only show in viewport if you also key the viewport visibility (but I am currently not sure if that's also possible...)